Yuanyuan Du

Rapid growth of industrial nitrogen fluxes in China: Driving forces and consequences

Human activities are strongly modifying the global nitrogen (N) cycle through increasing input, N species diversity, and pool size of industrial reactive N (Nr). However, the fluxes, fates and environmental consequences of industrial Nr (excluding synthesized N fertilizer) remain poorly understood and quantified. We report here that industrial Nr flux has increased 13.4-fold over the past 30 years in China, reaching 3.7 Tg N (1 Tg = 1012 g) in 2008, accounting for over 50% of China’s food Nr flux. Socioeconomic development (per capita GDP, urbanization and household size) significantly drives the growth of industrial Nr fluxes. This leads to “hotspots” of industrial Nr, mainly in relatively developed Eastern China. Industrial Nr loss rate during production is only 5%, much lower than that of cropland (50%) and livestock (80%). However, industrial Nr loss is point source pollution, and Nr release in concentrated doses produces serious risk in small regions. The contribution of structural N to total industrial Nr with a lifespan longer than one year (e.g., synthetic fiber, plastic) increased from 20% in 1980 to 70% in 2008. There was about 2.6 Tg N structural industrial Nr accumulated in human settlements in 2008, which could be one explanation of an unknown Nr sink of anthropogenic Nr input (mainly Haber-Bosch N fixation). Legacy effects caused by structural N accumulation have long-term consequences for environmental and human health, although structural N delays Nr release and reduces short-term Nr pollution. Industrial Nr use generates new features of modern global N biogeochemistry, such as increasing Nr species diversity, reducing Nr turnover rate. Future dynamics simulation of the earth system should involve industrial Nr. Explicit consideration and accounting of the fluxes and environmental consequences of industrial Nr would provide decision-makers a novel view of regional sustainable development.

Estimating irrigation water demand for green spaces in humid areas: seeking a sustainable water management strategy

Abstract Quantifying the irrigation water demand of green spaces (IWDG) is an important part of smart urban water management. However, the IWDG in humid cites is not well characterized. Moreover, the alteration of natural hydrological processes caused by urbanization leading to the dependence of green spaces on irrigation is becoming more common. To better understand the IWDG in humid areas, we developed an estimation model and used the Yangtze River Delta in China as a case study. Results showed that the amount of water required by the green spaces in the Yangtze River Delta was approximately 354 × 106 m3, which was equivalent to 12% of the urban residential water consumption in 2011. This study also investigated the spatial-temporal changes of urban green spaces and estimated their effects on irrigation water demand. These findings provide policymakers an integrated view of the water demand of green spaces associated with sustainable management.

Recoupling Industrial Dairy Feedlots and Industrial Farmlands Mitigates the Environmental Impacts of Milk Production in China

Dairy production is becoming more industrialized globally, especially in developing countries. The large amount of animal wastes from industrial feedlots cannot be fully used on nearby farmlands, leading to severe environmental problems. Using China as a case study, we found that most dairy feedlots employ a semicoupled mode that only recycles solid manure to farmlands, and only a few dairy feedlots employ a fully coupled mode that recycles both solid and liquid animal manure. To produce 1 ton of milk, the fully coupled mode could reduce greenhouse gas (including carbon dioxide, methane, and nitrous oxide in this paper) emissions by 24%, ammonia emissions by 14%, and N discharge into water by 29%, compared with the semicoupled systems. Coupling feedlots with constructed wetlands can further result in greater mitigation of N leaching into groundwater. However, the fully coupled system has not been widely used due to the low benefit to farmers and the institutional barrier that the feedlot owners have no right to use adjacent farmlands. Since a fully coupled system improves net ecosystem services that favor the public, a policy that supports removing the economic and institutional barriers is necessary. Our approach provides a template for mitigating environmental impacts from livestock production without sacrificing milk production.